Elevator control

ABSTRACT

A commanded position signal generator adapted for position based servocontrols as applied for example to elevators wherein the commanded position at which the controlled object will stop while subject to constraints of constant jerk, constant maximum acceleration, and constant maximum velocity is indicated through accelerating and constant velocity intervals. Stopping distance computation is performed in a first computation mechanism throughout the interval the commanded position signal is operating in an accelerating mode. Means recognize the mode of commanded position signal generation which is currently effective. As acceleration is curtailed to bring the commanded position signal into a constant velocity mode, a storage mechanism maintains the final maximum acceleration mode computed stop position for the pattern as the position at which the pattern would stop. During the constant maximum velocity mode of the commanded position signal, another computing mechanism indicates the predicted stop position. Each predicted stop position signal is compared to the signals for stops requested by registered calls for service and when a desired relationship between the predicted stop position signal and the call position signal exist the stop of the commanded pattern is initiated. Generation of a precise commanded position signal during the terminal portion of a run is enhanced by shifting from an initial position base for the signal to a final position base at a point in the signal generation when no discontinuity is encountered.

United States Patent nu 3,612,220

[72] Inventors Donl van L. Hall; Primary Examiner-Gris L. Rader Richard C- Losllbollgh; Ger ld 1 Assistant ExaminerW. E. Duncanson, Jr. Robaszklewicz, all of Toledo, Ohio Attorney-Wilson & Fraser [2]] App]. No. 872,184 [22] Filed Oct. 29, 1969 ABSTRACT: A commanded position signal generator adapted [23] Division of Ser. No. 380,385, July 6, 1964, for position based servocontrols as applied for example to 7 V Patent No. 3,523,232 elevators wherein the commanded position at which the con- [45] Patent ed Oct. 12;"1'971 "u" "m WW trolled object will stop while subject to constraints of constant [73] Assignee The Reliance Electric and Engineering jerk, constant maximum acceleration, and constant maximum Company velocity is indicated through accelerating and constant Cleveland, Ollo velocity intervals. Stopping distance computation is performed in a first computation mechanism throughout the interval the commanded position signal is operating in an ac celerating mode. Means recognize the mode of commanded position signal generation which is currently effective. As acceleration is curtailed to bring the commanded position signal into a constant velocity mode, a storage mechanism maintains the final maximum acceleration mode computed stop position for the pattern as the position at which the pattern would stop. [54] g gfm During the constant maximum velocity mode of the commanded position'signal, another computing mechanism in- 52 s (1 137/29 R dicates the predicted stop position. Each predicted stop posi- 5 1 B66]; 1/30 tion signal is compared to the signals for stops requested by re- [50] FieldolSearch 187/29 gi calls f r r ic and when a desired relationshi between the predicted stop position signal and the call position signal exist the stop of the commanded pattern is in- [56] adult CM itiated. Generation of a precise commanded position signal UNYTED STATES PATENTS during the terminal portion of a run is enhanced by shifting 3,l46,8$7 9/1964 Bosshard 187/29 from an initial position base for the signal to a final position 3,350,612 10/1967 Hansen et al. 3 [8/ I43 base at a point in the signal generation when no discontinuity 3,4l4,088 l2/l968 Bruns etal l87/29 is encountered.

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DONIVAN L. HALL RICHARD C. LOSH OUGH BY GERALD D. ROBA KIEIICZ affl g ELEVATOR CONTROL This invention relates to positioning controls and more particularly as illustrated herein to controls for determining the position of a movable body such as an elevator. This application is a division of Ser. No. 380,385 for Elevator Control filed July 6, I964, now U.S. Pat. No. 3,523,232.

l-leretofore it has been known to control the position of movable bodies by establishing a command signal to which the driving element for the body responds. These systems have included some means to ascertain the position of the body and indicate to the driving means the difference between actual position and commanded position. As applied in the machine tool art a number of means for generating position commands have been undertaken including punched tapes which control the steps in the drive elements for positioning the tool or body upon which the tool is working, magnetic tape records of control patterns, pattern developing devices which follow a particular physical configuration in the manner of a pantograph and fixed program devices which issue steps on a time basis or on a positional step by step basis. In this type application the values of velocity and acceleration ordinarily are not precisely defined. Further relatively sharp transitions in velocity and acceleration as are tolerable in the limits of the operating tools or equipment are permitted and frequently that as sought in the interest of expediting the processing by the tools. In some operations such as rolling mills even final position is not critical.

The present invention is illustrated as applied to elevator systems wherein much effort has been expanded with respect to providing means to automatically position elevator cars. Past efforts in this area generally have followed a philosophy of utilizing timed steps discretely issued to an elevator hoist motor to control that motor. Such steps ordinarily are responded to rather sluggishly in order that they are not reflected in the riding characteristics of the elevator. A paramount consideration in high quality elevator service is the comfort of the passengers. These considerations impose limitations on the tolerable acceleration and rates of change of acceleration which can be applied. Also an elevator must be precisely positioned so that its floor is level with the landing threshold at which passengers are given the opportunity to transfer between the car and the landing. Floor-to-floor time is a major criteria of high-caliber elevator service and maximum smooth acceleration is sought in achieving these rapid floorto-floor times. The loadings imposed upon elevator controls extend over a wide range. They include in a counterbalanced elevator car, balanced loading, loading in excess of balance through a range from balance to full capacity and loadings less than balance over a substantial range. Thus in some instances the elevator car tends to overhaul the drive. In other instances the drive is required to haul the load. These loadings can occur in either direction of travel and therefore in the past have greatly complicated the problem of attaining uniform high quality operating characteristics for all ranges of loading and all directions of travel. Attempts have been made to apply controls employing potentials representing desired position and potentials representing present position to elevators. Graham, U.S. Pat. No. 1,970,304 of Aug. I4, 1934 for "Elevator and Like Apparatus," discloses a motor driven potentiometer as a call position indicator wherein a call causes the potentiometer contact to be driven against a mechanical stop which defines the effective location of the deadman. The elevator position controls a potentiometer which is connected into a bridge with the call location potentiometer. A given potential difference turns the hoist motor on to cause the car to be carried toward the call and to progressively reduce that difference. As the potential difference is reduced below a predetermined level a switch is operated to slow the hoist motor and when the car position potential balances the call position potential the car is stopped.

The Graham type of control offered only course control of motor speed, responded to but one call at a time, it could not respond to supplemental calls which it passed in traveling to the call which placed it in operation, and it was quite inflexible.

A somewhat more refined control for elevators is disclosed in Bruns U.S. Pat. No. 2,699,226 of .Ian. 1 1, I955 for Elevator Control System. Bruns proposed balancing the signals from potentiometers representative of effective car position and call positions. The effective car position was defined by an actual car position potential plus an advance potential developed by ainotor driven potentiometer which in essence placed the potential representative of car position in advance of actual car position an amount sufficient to permit the slowing and stopping of the car at a call producing a matching potential. The advance potential also determined the operation speed steps in a motor controller by actuating switches.

Systems of the type described require precise mechanical drives. They are relatively slow to respond to changed conditions. They do not lend themselves to continuous control of an elevator hoist motor but rather employ steps of control which must be damped if an acceptable ride is to be obtained. Their operation is rigidly defined for a given system and requires substantial redesign and engineering for each system to which they are applied. They are bued upon car position to determine their command signals.

A preferred elevator motor control has been a direct current motor having a variable voltage source for its armature and a shunt field winding that can be energized at a constant level or within some limited range of variation to provide speed control. This type of control has been subjected to much refinement and to the superposition of auxiliary equipment in an effort to achieve optimum and uniform riding characteristics. These have included numerous compensation means for variations in load, speed signal developing means which are fed back to the motor control, variable-braking means dependent upon motor speed, supplemental motors to absorb some of the load torque particularly as the car is brought to a landing and regulating generators responding to many of the factors noted above including speed, loading and direction of travel.

Frequently such variable voltage controls have been adjusted to incipient instability in an effort to achieve the maximum characteristics wherein adjustment has been critical, requiring the efforts of highly skilled personnel to adjust and frequently readjust the system. Further, apparently identical lifting motors and lifting motor controls oflen require different adjustments and provide different operating characteristics under identical conditions. These systems have been sensitive to temperature variations, to brush and commutator condition, to brush position and to aging.

It is an object of the present invention to generate a precise pattern for the positioning of a movable body as a function of time.

Another object is to selectively constrain the position pattern utilized in controlling the motion of a body to selectable values of velocity, acceleration and rate of acceleration.

Another object is to selectably establish maximum first, second and third time derivatives of displacement for a movable body.

A fourth object is to control precisely the position with respect to time of a movable body in response to a command signal.

A fifth object is to minimize the flight time between a starting and terminating position for any selected amount of travel and combination of a wide range of selected maximum velocity, selected acceleration and selected rate of change of acceleration of a movable body.

Another object is to increase the accuracy of the determination of stopping distances for any length of run of a moving body.

A seventh object is to enable a moving body to respond to a signal requiring its stop or deceleration while in transit and up to the last possible instant that the body can respond to that signal within the constraints of the velocity, acceleration and rate of change of acceleration imposed upon the system.

An eighth object of the invention as applied to elevators is to accommodate any travel of an elevator between landings over any length of total travel.

Another object is to simplify the adjusting procedures required to establish the operating parameters of a system driving a movable body.

Another object is to stabilize the conditions imposed upon a control system for a moving body whereby drifi of operating characteristics and deterioration of such characteristics with time is avoided.

Another object is to suppress or eliminate the effects of un balanced load, hysteresis, nonlinearities of elements, deviations due to manufacturing tolerances and the efi'ects of temperature and line voltage variations on the control of elevator hoist motors.

A further object is to enable any of a plurality of different driving devices to be controlled by a common type of pattern control, and particularly as applied to elevators to enable the substitution of elevator hoist motors of various ratings in accordance with the dictates of the specifications applicable to the elevator installation with asuranee that the control will afford operating characteristics up to the limits of the capability of the hoist motor.

In accordance with the above objects, one feature of this invention involves a displacement vs. time pattern signal generator having internal logic and programming to mathematically integrate preselected limiting values of the first, second and third derivative of displacement to generate the optimum position command signal for such values. Included within the signal generator are limiting means to define the maximum levels of velocity, the A first derivative of displacement, acceleration, the second derivative of displacement, and rate of change of acceleration, the third derivative of displacement.

A second feature of the invention involves a stopping distance computer including logic means for accepting or rejecting stopping command received while the movable element responding to the displacement vs. time computer is in transit. The position of the body relative to the location along its path of travel of the stop for which the stopping command was issued, the velocity of the body and the limitations on acceleration and rate of change of acceleration are considered in the logic decisions involved in ascertaining the stopping distance. This computer accommodates any state of movement in which the body may be at the time the moving body should accept or reject a stopping command, that is, the body can be moving at its maximum velocity, it can be in its accelerating condition, and it can be changing its acceleration. In each of these circumstances the stopping distance computer takes into consideration the velocity of the body and the limits on the acceleration which can be imposed and the rate of change of acceleration which can be imposed so that the transition to a stopping mode is made at the last possible instance, thereby insuring that the most rapid transit available within the constraints imposed upon the system will be realized.

Another feature resides in equipment for determining the optimum point as the command signal approaches the stop to transfer from an initial positioned based command signal to a final position based command signal and means for effecting this transfer without discontinuity in the command signal as issued to the driving means.

Another feature resides in matching the equipment of the aforenoted features with existing elevator equipment to provide a compatible system having a wide range of applicability.

An additional feature involves a closed loop position servosystem for an elevator hoist motor employing unique compensating networks to, stabilize the system with needed DC gain and to provide the required bandwidth with adequate phase margin to force the elevator to accurately reproduce the computed position command signal.

One embodiment of the invention illustrating the above and additional features comprises an elevator system including an elevator car serving a plurality of landings in response to the registration of calls for sentice. The elevator car is driven by a direct current motor having a separately excited shunt field and a variable voltage supply for its armature. One suitable supply is a Ward-Leonard system including a direct current generator having its armature connected to the motor armature and a shunt field which is supplied from a suitable source such as a group of controlled rectifiers. Phase control of the rectifiers is provided by a firing circuit which enables both the direction and magnitude of current in the shunt field to be controlled.

An amplifier provides a signal which controls the firing circuits and is coupled with a compensator effectively comprising two lag-lead networks, and two lead-lag networks, one of which can be supplanted by a hoist motor speed feedback signal, to provide the proper phase and gain of the signal as a function of signal frequency whereby the DC gain can be at a high level. Control of the signal is by means of a position error signal. Hence the DC gain of the forward loop must be sufficient to reduce the position error of the elevator car caused by unbalanced loads to acceptable limits.

The error signal is in the form of a voltage derived from the comparison of a car position voltage and a position as a function of time command voltage. The car position voltage can be developed in a potentiometer driven by car motion as by a cable coupling to the car and may be in the form of a helix having its contactor driven in a helical path relative to its card. The command voltage is generated in a computer.

Position as a function of time is computed by developing a potential difference between an initial car position voltage, X and a call request voltage, X which is characteristic of the voltage the car position potentiometer would issue if the car were at the location of the request. The sign of this difference voltage indicates the direction of the call from the car, positive being above and negative below. The effective magnitude of this voltage is limited by a bidirectional clamp circuit which fixes an absolute level characteristic of the maximum velocity of the elevator car. This velocity limit can be adjusted by ad justment of the clamping circuit. The clamped signal results in a stepped input which is integrated and clamped by a second clamping circuit to produce a ramp. The slope of the ramp represents the acceleration constraints, both positive and negative, and can be adjusted by adjustment of the clamp voltage level. The ramp signal is difierentiated to produce a step signal subject to the velocity and acceleration constraints and this signal is integrated subject to limits imposed by a third clamp which defines the positive and negative limits on the rate of change of acceleration or jerk" to produce a ramp signal to and from the acceleration limit which signal persists for the period required to generate the velocity limit. This signal is the command signal acceleration pattern.

The command signals are derived from the acceleration pattern as a velocity as a function of time by integrating the signal with respect to time and as a displacement as a function of time by a second integration with respect to time.

ln order to achieve the requisite landing accuracy the base for the command pattern is shifted to the destination signal at a time when the transfer can be made without a discontinuity in that signal. The command pattern as generated above results in an initial period of constant rate of change of acceleration to a maximum acceleration which continues for a second period until the predetermined maximum velocity is approached, a third period of transition from maximum acceleration to maximum velocity at the rate of change of so celeration, a period of constant velocity, as slowdown is initiated, a fifth period of constant rate of change of acceleration to a maximum negative acceleration, and a period of maximum negative acceleration. Rather than make the transition from maximum negative acceleration to zero velocity at the prescribed rate of change of acceleration, at the time this change is to occur the pattern is transferred to a signal based upon its distance from the destination and permitted to approach the destination signal level as a function of time, for example as an exponential decay.

The above-described pattern can be modified while retaining the constraints of acceleration and rate of change of ac celeration for a displacement command less than that required to achieve maximum velocity. When slowdown is initiated during acceleration, the rate of change of acceleration continues through new acceleration in a smooth transition to negative acceleration.

The elevator control of the illustrative embodiment employs the above-described command signal with a stop time computer which permits optimum patterns within the acceleration, velocity and rate of change of acceleration constraints imposed. This computer generates a stop position signal and compares it with the destination signal so that the creation of a predetermined relationship of those signals initiates a stopping operation. Three stopping modes are possible: one from maximum velocity, one from acceleration, and one from the transition between acceleration and maximum velocity. The latter form of stop is treated in the same manner as a stop from maximum velocity since the rate of change of acceleration constraints carry the command signal through the maximum velocity if the stop is initiated during that change. In that stopping operation the command continues to change at the defined rate from a positive to a negative acceleration.

A stop from maximum velocity is computed by storing the displacement signal generated in achieving maximum velocity and comparing that signal with the distance remaining to be traversed. This distance is ascertained by subtracting from the destination signal the pattern position signal. When the monitored difference equals the stored signal the transition to deceleration is initiated.

A stop from acceleration is computed by continuously generating the instantaneous stopping position signal during acceleration and comparing it with the destination signal. This computation is made in terms of the initial position signal for the run, the current command signal position, the current command signal velocity, the maximum acceleration setting, and the maximum rate of change of acceleration setting.

The sensing of the destination signal is arranged to enable the command signal to respond to any service demand encountered for a stopping station to which the elevator can be brought to a stop within the acceleration and rate of change of acceleration constraints. At the initiation of a command signal generation, a predetermined station is designated as the destination and a signal therefor generated. Conveniently, a terminal landing can be the destination. As the command signal develops, the stop registering devices for its range of response are sampled. Thus if a command signal has developed two landings of displacement and the computed stopping distance at this moment is two landings, the calls for the fourth landing from the initiation position will be monitored at that moment. If a call is sensed, the system accepts it and initiates a stop sequence for the command signal. If, however, the call was imposed afier the elevator could be stopped within its acceleration and rate of change of acceleration constraints, the call would be rejected and the pattern would continue to develop. Once a call is accepted, the destination signal is transferred to the landing of that call and is held until the car has stopped in response to the command signal.

The above and additional objects and features of this invention will be appreciated more fully from the following detailed description when read with reference to the accompanying drawings in which:

FIG. I is a functional block diagram of an elevator control system utilizing this invention;

FIG. 2 is a functional block diagram of a command signal generator for producing a signal representative of computed position as a function of time;

FIG. 3 is a schematic diagram of an AND circuit and Schmitt trigger employed together for AND logic and an OR circuit as represented by the logic symbols of FIGS. 3a and 3!: respectively;

FIG. 4 is a schematic of a differential amplifier, and the logic symbol for such an amplifier is shown in FIG. 4a;

FIG. 5 is a schematic diagram of chopper stabilized amplifier utilizing in part logic symbols, and FIG. 5a is the logic symbol for such an amplifier;

FIG. 6 is a schematic diagram of a transistor power switch and FIG. 6a is the logic symbol employed therefor;

FIG. 7 is a schematic diagram of an amplifier and Schmitt trigger combined to indicate the presence or absence of an absolute value of a signal and arranged to adapt certain of the signals to the logic functions utilized in the circuits set forth;

FIG. 8 is a schematic diagram of a buffer amplifier to adapt certain signals to the logic functions;

FIG. 9 is a xhematic diagram of a command signal generator according to this invention as depicted in FIG. 2 and utilizing logic symbols as illustrated above;

FIG. 10 is a plot against time of velocity, certain relay functions entering into the logic of this control, and a number of voltages as they appear at various positions in the command signal generator shown in FIG. 9, as those waveforms appear for a full speed run;

FIG. 1 l is a series of curves corresponding to those of FIG. 10 for a short run where full speed is not reached;

FIG. 12 is a block diagram of the stopping distance computer according to this invention as it is combined with the command signal generator of FIG. 9;

FIG. 13 is a schematic diagram of the stopping distance computer of FIG. 12;

FIG. 14 is a schematic diagram of an acceleration definer utilized in marking the end of acceleration on the signal generated by the signal generator of FIG. 9;

FIG. 15 is a schematic diagram of means programming the control during changes in acceleration;

FIG. I6 is a plot against time of the slowdown distance, the displacement, the velocity, the acceleration and the rate of change of acceleration for a typical elevator controlled according to the present invention;

FIG. I! is an across-the-line diagram of certain relay circuitry utilized in adapting the logic circuitry of the previously described elements to existing elevator controls;

FIG. I8 is a call checking and accepting circuit schematic for an elevator control utilizing the command signal generator and stopping distance computer of FIGS. 9 and I3; 2

FIG. 19 is a block diagram of a position loop control as applied to an elevator control;

FIG. 20 is a compensation network as utilized in the system represented in the block diagram of FIG. 20;

FIGS. 21 through 24 are plots on a semilogarithmic basis of gain and phase shift plotted against frequency in radians per second to show the open loop characteristics of an elevator system to which this invention might be applied; and

FIG. 25 is a semilogarithmic plot of relative gain against frequency in radians per second showing the characteristics achieved in an elevator system utilizing this invention.

The present invention has been illustrated as applied to an elevator system functionally depicted in the block diagram of F IG. 1. In that system a hoist motor 31, which advantageously from the standpoint of speed control can be a DC motor having a separately energized shunt field winding and an armature supplied for speed control from a variable voltage source, drives an elevator car 32. Car 32 is counterweighted as at 33 to compensate for some suitable portion of the rated load of the car, ordinarily 40 percent of rated load, whereby the load is fully counterweighted when loaded to 40 percent of capacity, is less than counterbalanced when loaded in excess of 40 percent, and is overbalanced when loaded to less than 40 percent of rated capacity. Control of hoist motor speed is determined from a variable voltage source 34 which in the discussion to follow will be a direct current generator having its armature driven from a suitable prime mover at a constant speed and its shunt field current varied to control the voltage it applies to the motor armature, in accordance with well-known Ward-Leonard principles. The shunt field of the generator may be supplied from any suitable source as for example a group of silicon controlled rectifiers having phase control firing circuits. Control of the firing circuits or other mechanism for establishing the current flow in the shunt field of the generator is afforded by an amplifier and compensator represented by the rectangle 35.

The amplifier and compensator are so arranged as to afford a relatively high forward gain and a controlled amount of phase shift, whereby the gain is attenuated at frequencies where the system tends to become unstable. The forward loop in which the amplifier and compensator operate extends from summing point 38 through a car position signaling means represented by the potentiometer 36 which issues a voltage on lead 37 representative of car position throughout all positions of travel of the car. The signal on lead 37 is introduced at summing point 38 and is combined with a command signal which commands a car position with time based upon the actuating impulses imposed upon the elevator system. This command is derived from the position pattern generator 39 over lead 41 extending into the summing point 38. From the summing point 38 the error signal resulting from the comparisonof the car position signal and the command signal is applied over lead 42 to the amplifier and compensator 35.

Details of the elements outlined above will be set forth in the following description. However, it should be recognized that control stimuli such as calls registered on the conventional car buttons located within the elevator car and those registered at landing buttons for the landings which the elevator car is capable of serving dispatchers for starting cars from stations, and such known features as stops for high car reversal, high call reversal, late car reversal and the like require flexibility in the form of the pattern to be generated. Stimuli placing the position pattern generator in operation can be considered a call request applied to the pattern generator over lead 43 from a call selector 44. The function of the call selector generally is to ascertain the location of landings along the path of travel at which service is required by the elevator car sufficiently in advance of the arrival of the car at the landing to permit the car to be slowed and stopped by a command position signal generated in the position pattern generator meeting the constraints of maximum velocity, maximum acceleration and maximum rate of change of acceleration set into the generator. The position of the call request or destination of the elevator is indicated to the pattern generator as a potential off the string of resistors 45 arranged as a potentiometer with fixed points corresponding to landing positions available to the input to the call selector. The potentiometer 36 and the resistor string 45 are supplied from the same power supply, not shown, connected to terminal 46 and have their opposite ends grounded.

The pattern computer normally remains dormant so long as its output signal represented as a voltage appearing on lead 41 is of the same level as the input voltage derived from the call selector 44 and applied on lead 43. If this input voltage differs from the output of the pattern computer, the computer will, subject to its own control, alter its own output until agreement has been reached. Typically the input will differ from the output only when a new floor position has been called for by the imposition of a demand for elevator service. Thus when a new floor voltage is connected to the computer, the computer generates the position-time pattern required to regain the equality of input to output. in the process the hoist motor for the elevator car is supplied a position-time pattern which it will follow to a new floor position. in advancing its output to the desired new value, the computer regulates the generated position-time pattern in such a manner that the first, second and third time derivatives of displacement are limited and subject to adjustment. The first derivative can be considered the command signal for velocity of the hoist motor and the car,

the second derivative can be considered the acceleration and the third derivative can be considered the rate of change of acceleration or jerk.

The negative feedback is the system afforded by applying the car position signal to the summing point in combination with the command position signal provides a high degree of accuracy in the positioning of an elevator subject to no unbalanced load. Since the system responds to an input displacement command, it regulates its output displacement accordingly by comparison of its output position to its input command and utilizes the amplification of the difference or error as derived from the summing point, unbalanced loads will cause errors. However, loop gain in a system utilizing position feedback reduces the displacement errors caused by unbalanced loads. Thus in this system gain requirements are set by the unbalanced load to be imposed upon the elevator and the amount of displacement from the landing that is tolerable for maximum unbalanced load. It is when the forward loop gain has been increased to a level reducing the amount of displacement for maximum unbalanced load or the position error for maximum unbalanced load to negligible levels that the system tends to become unstable unles compensators are utilized. Compensation can be obtained by employing suitable lag-lead and lead-lag networks or a combination of lead-lag and lag-lead networks in a composite network.

In the system under consideration suitable accuracy is obtained as to car position by the use of a multitum potentiometer corresponding to the potentiometer 36 coupled to the elevator car as by means of a driving cable from the potentiometer to the car to cause rotation of the potentiometer contactor as the car is moved along its path of travel. While the potentiometer has been proposed, it is to be understood that any scheme which could provide a voltage or voltage ratio proportional to car position would be satisfactory in a system of this nature provided stability and resolution were compatible with a requirement of at least plus or minus one-tenth inch positioning accuracy.

Before considering the position time pattern generator a general discussion of the operating theory of a position pattern will be presented. A primary consideration in this presentation is the comfort and safety of human being conveyed by the moving equipment. Therefore this pattern and the limitations imposed thereon are presented in terms of its utilization with an elevator. However, it is to be appreciated that the general concepts involved are not limited to elevators and have a substantially greater range of application. For example, they can be employed in train control operations or the pattern can be modified to adapt it to suitable machine control functions.

An examination of the possible transitions of pattern voltage where pattem voltage represents position reveals immediately that a transition at a linear rate representing constant car velocity could not be tolerated since the initiation and termination of the motion commanded would require infinite acceleration. Therefore a transition should include a period of acceleration at the initiation of motion and a deceleration at the termination of motion. Passenger comfort dictates that acceleration must not exceed some limits. ln elevator applications 4 feet per second per second is considered quite acceptable. If extremely low accelerations are employed, changes in velocity will be imperceptible. However, in the interest of utilizing the elevator equipment effciently by completing the run between two stations as rapidly as possible, high rates of acceleration should be employed.

With a finite and constant acceleration, however, the rate of change of acceleration or jerk" at the initiation and termination of the acceleration periods would be infinite. This also creates an uncomfortable and possibly dangerous condition. Accordingly, a further constraint is that the rate of change of acceleration must be finite and not exceed a selected limit. Again in the interest of efficient utilisation of equipment, a rapid rate of change of acceleration should be employed. A rate of 8 feet per second, is acceptable for elevator applications.

in elevator utilizations excellent riding characteristics can be achieved employing a constant jerk or rate of change of acceleration from zero speed through a transition period to a period of constant acceleration until the maximum velocity is approached, at which point a constant negative value of rate of change of acceleration is utilized to enter the constant maximum velocity portion of the run. Once full speed has been attained, it is maintained until it is appropriate to initiate the slowdown, such slowdown being accomplished by a transition at a constant negative rate of change of acceleration to constant negative acceleration which is permitted to extend over a period necessary to approach zero speed and the transition from this negative acceleration to zero speed can be made at a constant positive rate of change of acceleration. A plot of velocity vs. time for this form of a pattern is depicted in the uppermost curve of FIG. 10. Advantageously, from the standpoint of symmetry in the control of motion where both directions of travel must be controlled, the absolute limits of rate of change of acceleration can have equal magnitude as can the absolute limits of acceleration and velocity. The curve referred to in FIG. may be integrated and the result can represent a command pattern for an ascending elevator car. A descending elevator car would have an inverted pattern around the origin. The lowermost curve in FIG. 10 corresponds to a plot of rate of change of acceleration or jerk and the next upper curve labeled E, represents acceleration under the jerk constraints, illustrating a linear rate of increase of acceleration to the maximum, a flatting and then the termination of acceleration at a linear rate to zero as the maximum velocity portion of the motion is approached.

These constraints imposed upon the system can be considered from a mathematical point of view in terms of displacement. Thus it should be recognized that velocity is the first derivative of displacement with respect to time, acceleration is the second derivative of displacement with respect to time and rate of change of acceleration or jerk is the third derivative of displacement with respect to time. Accordingly, if the optimum jerk curve, the curve of the third derivative of displacement with respect to time, is integrated, an acceleration curve subject to velocity, acceleration and jerk constraints corresponding to the plot E in FIG. 10 will be obtained. An integration of the acceleration curve corresponding to the curve labeled E, in FIG. 10 produces a velocity curve subject to velocity, acceleration and jerk constraints. A third integration yields a displacement vs. time function with it again meeting the constraints of jerk, acceleration and velocity.

In FIG. 2 a functional block diagram of a position vs. time pattern or command signal generator is illustrated. This system is represented as an acceleration generator 51 which generates a voltage signal corresponding to signal E,, of FIG. 10 for a full speed run and where maximum velocity is not attained E, of FIG. 11. The acceleration generator is subject to constraints of jerk imposed upon lead 52, acceleration applied from lead 53, and velocity applied from lead 54. It issues over lead 55 a voltage representing acceleration which is applied to a first integrator 56 to produce a velocity time function of the form shown in the uppermost curve of FIG. 10. This voltage signal is applied over lead 57 to a second integrator 58 which produces the desired position vs. time voltage form on lead 41 as utilized at the summing point 38 shown in FIG. 1.

A detailed schematic diagram of the position vs. time signal generator is set forth in FIG. 9 employing a number of logic symbols in place of the detailed circuit elements. Accordingly, before proceeding with a discussion of this schematic the individual elements corresponding to those logic symbols will be disclosed.

In FIG. 3 a schematic diagram is shown of a circuit which with minor modifications can be utilized as either an AND represented by the symbol in FIG. 3a or an OR represented by the symbol in FIG. 3b. When functioning as an AND, the double pole single throw switch DPST is left in the position shown whereby terminals 61 and 62 function as typical AND inputs. To condition the system as an OR, the switch DPST is transferred to its second position whereby the tenninal 62 is grounded and terminal 63 is placed as a parallel input with terminal 61 to constitute with 61 two typical OR inputs. The AND circuit as utilized below is a composite of an AND controlling a Schmitt trigger made up of the circuit to the right of junction 60 in FIG. 3 and represented in FIG. 30 as a separate rectangle. The Schmitt trigger is not essential to the OR functions; hence it is frequently restricted to the junction 50 as its output and is so illustrated by the symbol of FIG. 3b.

Each of the AND and OR input terminals is connected through a diode 64 and a resistor 65 to a minus 12 volts supply (not shown) as at terminal 66 and in the case of the AND to a Schmitt trigger through suitable conditioning diodes 67 and 68 to a voltage divider made up a resistols 69 and H to the base of transistor 01. Transistors Q1 and Q2 are the active elements of a Schmitt trigger providing an on" output lead 72 and an "inverse" or "ofl'" output lead 73 represented for an AND function in FIG. 34 by the lead extending from the main portion of the square symbol and the lead extending from the cross hatched comer of the main symbol respectively. On" input and output signals from this circuit are represented by a grounded state while an essentially l2 volt collector bias is an off signal. Thus if a ground is absent from any of the AND inputs, transistor 01 is conducting and the output lead 73 is effectively at the grounded level to provide an on on the inverse output. At this time the voltage divider formed from the minus 12 volt supply terminal 74 through collector resistor 75, resistor 76, the base of Q2 and resistor 77 maintains the base of Q2 essentially at ground and therefore Q2 nonconductive so that the nonnal output 72 of the AND circuit is at the collector potential and effectively otF'.

When all of the input tenninals in the AND circuit are grounded, transistor 01 is turned off and the AND output lead 73 is at the efiective collector potential of minus I2 volts less the drop in resistor 75 or the off condition. Under these conditions, the base of transistor 02 is sufficiently negative to place that transistor in its "on" condition so that its collector potential is essentially at ground and output 72 is in the "on" or grounded state.

When set for operation as an OR circuit with switch DPST closed, a ground imposed on any of OR inputs 6I, 63 or their equivalent transfers junction 50 from the -12 volts applied at terminal 66 to ground thereby ofl'ering an "on" output from the OR to any following logic elements.

FIG. 4 is the schematic diagram of a differential amplifier represented by the logic symbol of FIG. 40. Plate voltage is applied to the two triodes 81 an 82 from a suitable source connected to the terminal 83, and cathode voltage is applied to both triodes at terminal 84. Each of the two tubes act as a cathode follower driving the cathode of the other tube. The output is derived as a potential across the terminals 85 and 86 and can be established without regard to ground. Inputs represented by the plus and minus signs in the symbol of FIG. 4a are respectively shown to the grids of tubes 8] and 82 from leads 87 and 88. This type of amplifier has a number of advantages including the ability to issue an output voltage either with or without sign reversal referred to the input voltage, and the ability to mix two voltages by taking their difference. As illustrated in the symbol of FIG. 40, when the output is taken from the lead 86 an inversion will be realized in the signal as applied to the input lead 88 while no inversion occurs when the input is applied at 87.

While differential amplifiers are self stabilizing to a substantial degree, where maximum stabilization is desired, their characteristics can be enchanced by chopper stabilization in the manner depicted in FIG. 5. The logic symbol for a chopper stabilized amplifier is illustrated in FIG. 5a. Chopper stabilization is achieved by connecting an inverting, high-gain, carriermodulated amplifier, whose output has been demodulated, between the positive and negative input as represented by the chopper modulated amplifier 91 connected from input terminal 92 to the positive input 93 of the conventional differential amplifier illustrated in FIG. 4. Input 92 is connected to the negative input of the amplifier 94 through condenser 95. Thus only one external input is available to a chopper stabilized amplifier as shown in the logic symbol of FIG. 5a and chopper stabilized output derived on lead 96 is inverted.

FIG. 6 represents a transistor power switch having a symbol utilized in the schematic diagrams as shown in FIG. 6a. The switch comprises a PNP transistor Q3 having an input 101 to its base through the voltage divider provided by series resistor I02 and ground resistor 103. The emitter of the transistor is connected through a diode 104 to ground. The collector is connected through the element to which the switch is applied, in the present application, relay coils, as at terminals 105 and 106 to a terminal 107 connected to a suitable source of collector voltage as a l 2 volt supply not shown. A diode 108 is connected across the switch load.

The circuit of FIG. 7 is utilized to provide an output signal as ground representing on on its normal output lead 111 and a l2 volt signal representing off" on its inverse output lead 112 any time a signal other than zero is present on its input lead 114. The absence of a signal on input lead 114 inverts the conduction states placing an on or ground signal on lead 112 and an ofi or l2 volt signal on lead 111. The amplifier comprises a section including transistors 04, 05, Q and Q7 which control a Schmitt trigger including transistors 08 and Q9 providing the outputs. The circuit will best be understood by a consideration of its operation.

When a positive signal with respect to ground is applied to input 114, transistors Q4 and OS are nonconductive. Since there is no drop in the collector resistors 116 and 117 of these transistors, the base of each of transistors Q6 and Q7 are at' l 2 volts and these transistors are placed in conduction. Since O7 is conducting, its collector and junction point 118 are essentially at ground. This ground prevents conduction in transistor Q8 since it is below the operating threshold which must be passed through diodes 119 to establish the threshold voltage imposed on the base of transistor Q8. The voltage divider composed of resistances 122, 123 and 124 establishes a negative bias on base Q9 which causes that transistor to be conductive. This effectively grounds collector Q9 since the collector voltage drop occurs in resistance 126, and terminal 111 issues a ground. This neglects the resistance of emitter resistor 121 which is small compared to collector resistor 126. Condenser 125 bypasses the resistor 123 and this speeds up" the switching action. The collector voltage at the collector of Q8 is'reflected in the inverse output 112 as an "off" signal.

Application of a negative voltage with respect to ground at input 114 causes both of transistors 04 and O to be conducti've by reducing the base potential sufficiently to exceed the emitter bias of diode 128 on Q4. This bias is developed in the path from bus 113 to ground afforded by resistor 127 and diode 128. Diodes 132 and 133 provide protection for the base-emitter junctions of Q4 and Q5. With Q4 and Q5 conductive, their collectors are at ground and transistors Q6 and Q7 are nonconductive. Junction 118 floats under these conditions and no signal is available to place transistor Q8 in conduction. Therefore the conditions described for a positive input at 114 prevail in the Schmitt trigger and ground appears at 111 while inverse output 112 is off.

If zero voltage is applied to input 114, it results in conduction in transistor Q5 while transistor Q4 is nonconductive. Under these conditions the voltage drop through emitter resistor 127 and diode 128 is such that emitter O4 is negative with respect to its base and that therefore the transistor is off, while transistor 05 has its emitter at ground and its base at a negative voltage due to the connection from bus 113 through resistance 130 and is conductive. This places base Q7 at ground while that of Q6 is at l 2 volts. Since transistor 07 has its emitter biased negatively with respect to ground through the voltage divider provided by resistor 129 and the forward drop of diode 131, O7 is nonconductive. Q6, however, is conductive and therefore imposes a base voltage on transistor Q8 which is determined by the ratio of the voltage drop in resistors 134 and 135, the forward drop in diodes 119, and the drop in resistor 136. This base voltage is sufficient to place I transistor 08 in conduction whereby the base potential on Q9 is reduced to make 09 nonconductive. Under these conditions a ground appears on inverse output lead 112 and a l2 volts appears on output 111.

The circuit of FIG. 7 thus monitors the absolute value of an input on 114 if that input is above a threshold level. It is termed an absolute value" circuit below and has been assigned the symbol in FIG. 7a where the inverse output issues from the comer'square with the crossed diagonals.

The buffer amplifier on FIG. 8 is employed in a number of locations in the system diagrams. It includes an input lead 141 and an output lead 142 which issues a ground signal when the input receives a signal which is positive with respect to ground and issues a negative voltage signal signifying an off output when the input receives a negative voltage with respect to ground. A positive voltage on 141 is applied through input resistors 143 and 144 to the base of 010 to insure that that transistors is nonconductive. The emitter of transistor 010 is connected to ground at bus 145. The emitter-base junction is provided with back voltage protection by the diode 146. The collector of Q10 is supplied with l2 volts at bus 147 through collector resistor 148. With transistor Q10 nonconductive, its collector is essentially at l2 volts and this voltage is applied to the base of transistor Q11 to cause that transistor to enter its conductive state. While conductive, the collector of transistor Q11 is esentially grounded since the preponderance of the collector voltage supplied from lead 147 is dissipated in collector resistor 149. Accordingly, the ground at the collector appears at the output lead 142 as an an on" signal.

Next consider the application of a negative signal at input 141. This signal, when applied to the base of 010, turns on the transistor to ground its collector thereby grounding the base of transistor 011. An emitter bias is provided for 011 through resistor 151 connected to lead 147 and voltage regulating diode 152, whereby the emitter is always maintained somewhat negative with respect to ground. In this condition of bias the transistor is nonconductive. Accordingly, the potential appearing on bus 147 is developed at output lead 142 to signify an off or negative output voltage signal.

The circuit is made insensitive to small reductions in posi tive input voltage at or near the "on" threshold by resistor 153 which requires a reduction of at least 10 per cent below the tum-on voltage to invert the conduction state.

The circuit of FIG. 8 is illustrated in a number of locations as a bufi'er amplifier in the schematic system diagrams and is symbolized as a rectangle labeled BA.

The position-time signal generator as shown schematically in FIG. 9 will now be considered. As indicated in the block diagram of FIG. 2, the first element of the position-time signal generator is an acceleration generator. The acceleration generator consists of two basically similar circuits. The first circuit combines the velocity and acceleration constraints. The second circuit imposes the rate of change of acceleration with time constraints.

A pattern is generated when a difference is indicated to the generator between the current position signal of the generator for the object being controlled, in the illustration, an elevator, and the position to which it is desired to transfer the object. In the elevator example, the existence of a call for service at a landing remote from that signal which the generator indicates is the current location of the elevator will produce such a signal. If the initiation or current position of the object as signaled by the command generator can be represented'by a voltage X, and the desired or destination location represented by a voltage X those two voltages can be applied through suitable resistors 16] and 162 to the positive and negative input terminals of differential amplifier Al. The amplifier mixes and amplifies the two voltages by taking their difference and issuing it as a signal through resistor 163 to junction 164 from which it is fed through resistor 165 to differential amplifier A2 positive input. The signal from junction point 164 is clamped by the action of diodes 168 and 169 connected thereto with reverse polarities and coupled to respective adjustable voltage sources 154 and of a polarity opposite that of the conductive direction through the diodes and of equal magnitude whereby plus and minus limits on the level of the signal representative of velocity can be imposed at the junction 164. The adjustable voltage sources are shown as batteries connected across potentiometers in the illustration although alternative forms of regulated limiting voltages are available.

The logic of the functions to be described below requires an indication of the existence of a velocity signal without regard to its polarity as derived from an absolute value circuit of the type shown in FIG. 7 represented as AVI in the drawing. Circuit AVl issues a signal when either a plus or minus difference exists between the input signals X, and X, to amplifier A1. Similarly, a buffer amplifier BAI corresponding to the amplifier shown in FIG. 8, is connected to the junction point 164 to issue an on signal for a plus velocity and an off signal for a minus velocity. A positive velocity indicates an "up" command signal while a negative velocity indicates an down" command signal. The existence of, and the polarity of, a difference of the signals X, and X and the resultant velocity signal are sensed at the junction I64 by these circuits. Further, this signal which represents the velocity to be commanded by the system is limited to a voltage proportional to the plus or the minus maximum velocity limits as set by the voltages applied to the diodes 168 and 169. For purposes of aiding the understanding of the logic circuits of FIGS. l3, 14, and 18, the signals from AVI have been indicated as IVI indicating an absolute value of V (without regard to sign) and from BAl as :V indicating a plus or minus value of V.

The velocity signal imuing from A2 is amplified in accordance with the gain of amplifier A2 as set by the value of resistors I66 and 167. Signal from A2 is passed through resistor 171, relay contact K2-l and resistor 172 to the chopper stabilized amplifier A3, from which it is fed back through resistor 173 to the input of diiTerential amplifier A2. Each of amplifiers A2 and A3 have a high gain. The resistors I65 and 173 provide a negative feedback loop with a feedback ratio B equal to iss l13+ l85 If the signal issuing from the output of amplifier A3 is designated E,, and the signal at the junction 174 between resistors I71 and I72 is designated E,,, it can be shown that E, is related to the velocity voltage V by the relationship If R equals R then E, equals for DC values of V. In the plots of E, in FIGS. 10 and II the curve has been inverted.

As at the junction I64, the signal E, at junction 174 is clamped by a pair of diodes 175 and 176 connected as in the case of diodes I68 and 169 to respective reverse poled adjustable voltage sources 156 and 157 to define voltages minus a and plus a characteristic of the plus and minus acceleration limits. In addition an absolute value circuit AV2 is coupled at junction 174 to provide an output indicative of the presence of an acceleration component in the pattern being generated and the inverse of the presence of an acceleration component. An acceleration component issues a ground on lead Ial and no component issues a ground on lead I'EI Thus the ability of the pattern generator when a step input is applied to follow the step input is limited by the clamping action of the diodes to plus or minus the magnitude of the voltage setting a. The capacitor 177 connected between the output and input of amplifier A3 provides an integrating function in cooperation with resistor 172 so that for a high gain amplifier A3 having a gain offrom ID to 10,

Since E, is limited to plus or minus a, the expression of E, becomes E, and therefore a will persist until E,,=V at which time E. becomes zero.

Plots of the various signals experienced in the circuit of FIG. 9 are shown in FIG. 10 for a displacement of sufficient magnitude to enable the moving object to attain its maximum rated speed. ThlB the signal isuing from amplifier A6 as a result of the combining of the input signals X, and X,.,, as limited by the diodes 168 and 169, is depicted as V on the curve. This signal when applied to the amplifier A2 produces a signal I5. at junction 174 as shown in the plot wherein E. ha a finite value during the period of acceleration and deceleration. Further the voltage E, as it imues from the chopper stabilized amplifier A3 appears as shown in FIG. 10 as an acceleration limited velocity curve with infinite rate of change of acceleration or jerlt at the initiation of the curve, I, at the brealtover to maximum value r, and on deceleration at the brealtover from maximum value at r. until a zero velocity is approached at t It should be noted that in the curve E, would be negative going due to the inversion in the amplifier and is drawn as shown only for clarity in illustration. If jerk limiting where not required, integration of the voltage E, would yield a position-time pattern containing limited velocity and acceleration and unlimited jerk.

After E, equals V has been reached and E, equals zero, a step of the input V to zero results in the previous cycle being repeated but with E, being clamped to the acceleration limit a of the opposite sign through one of the diodes I75 and 176. This deceleration cycle occurring between intervals times t and t. appears as a negative E, of magnitude minus a on the plot of FIG. 10.

The area under the E, vs. time curves is directly related to the top speed commanded, that is, E, and V. Also, if the initial and final values of E, equal zero, the area of acceleration equals the area of deceleration with appropriate correction of the sign of the areas.

In order to meet the constraint of a selected finite value for the rate of change of acceleration, the acceleration vs. time plot must appear as shown at E, in FIG. 10. That is, it must have an initial and a final slope to its maximum rate of acceleration defined by the magnitude of E, in order that an object moving in response to the signal will be gradually brought up to the acceleration level dictated, and gradually transferred from the acceleration to a constant velocity. In order that the commanded top speed of the signal be maintained, the area under the newly formed curve should be the same as that under the original E,, This can be observed by inspection of E, and E, on FIG. I0 inasmuch as the curves are of equal area.

The jerk limited acceleration pattern is attained using the same type of circuitry as used to obtain the acceleration limited velocity voltage E, Thus E, is passed from junction point I74 through normally closed relay contact RF-I, input resistor 178 into chopper stabilized amplifier A4 having a gain adjusting resistor I79 connected between its output and its input. The output of amplifier A4 is also connected through relistor III to the input of an inverter differential amplifier A5 also having a gain adjustment resistor I82 connected from its output to its input. From the output of AS the signal is passed through resistor I83 to junction point 184.

THe signal follows a number of paths from the junction 184 including that through resistor 185 to amplifier A6 functioning as an integrator by virtue of capacitance 186 connected between its output and its input and also supplying through feedback resistor 187 an input to the amplifier A4 whereby the circuit between A4 and A6 has characteristics similar to those of the circuit between A2 and A3. Jerk limiting of the signal is achieved at junction point 184 by means of diodes 188 and 189 connected to adjustable sources 158 and 159 of negative and positive DC voltage whereby the signal limits representing the rate of change of acceleration with time or jerk as symbolized by b can be imposed upon the system in an adjustable manner by the appropriate setting of the potentiometers. The interval of the change in the acceleration, i.e., the interval during which jerk is present, is also monitored at the junction point 184 by absolute value circuit AV3 having a normal output |bl indicating the existence of jerk and an inverse output lbl indicating the absence of jerk, each of these outputs being effective to issue a ground signal in the on condition and a negative voltage signal in the off condition.

Referring to the curves of FIG. 10 the signal at the output of amplifier A6 is shown as curve E It is this signal that is fed back negatively to the input of amplifier A4 and represents a jerk limited acceleration pattern which can be independently adjusted by varying the clamping voltages a for acceleration, b for jerk and V for velocity at junction points 174, 184 and 164 respectively. The waveform at the junction point 184 with jerk limiting imposed is shown on the plot E, of FIG. 10.

Two integrations of the jerk limited acceleration pattern F, yields a position-time pattern voltage meeting all requirements of jerk, acceleration and velocity limiting. As developed in the present circuits, these limits are independently adjustable by varying their clamping voltages a, b and V.

The signal 15, isuing from amplifier A6 as presented in FIG. 10 has been inverted for clarity in relating it to acceleration. Thus that area on the positive side of the origin is in the circuit negative and that on the negative side is positive. That signal is applied to an integrator comprising resistor 19], a chopper stabilized amplifier A7 and capacitance 192 to produce a signal having the form of a velocity command vs. time at terminal 193. This signal has been designated as X,, as the first derivative of displacement, and it has the waveform corresponding to the velocity vs. time plot of FIG. 10 in all but the final interval extending from time t, to time t,. This termination of the velocity pattern at this time is due to the operation of relay RF to close contact RF-3 as will be discussed below. The effective amplification level of integrator A7 may be adjustable where it is required to relate or scale the signal values derived therefrom with the feedback values obtained from the driving system for the object being controlled. In the case of an elevator utilizing a position feedback signal as derived from potentiometer 36, the magnitudes of X, can be adjusted at integrator A7 to provide the proper relationship.

The second integration of the signal E, is accomplished in the integrator connected through normally closed relay contact RF-4 and comprising resmtor 195 to the input of chopper stabilized amplifier A8 having its output connected to its input through the capacitance 196. The output of this integrator as it appears at terminal 197 is a plot of position vs. time at suitable voltage levels obtained through the adjustment of the gain of integrator A8 (by means not shown) to match the position voltages derived from the feedback loop of the driven device. This position vs. time signal has been inverted by the amplifier function and is represented at terminal 197 as minus X,.

The present system contemplates accuracies in the control of a moving body of the order of one-tenth of an inch in a total travel of the car. While as shown above the integration of jerk, acceleration and velocity can be programmed to generate the required position vs. time command signal where these levels of accuracy are required it cannot however be expected to be errorless. In order to overcome these errors, even if they be about 2 or 3 inches over the proposed range of travel, the command signal can be based from the destination position rather than from the initiation position provided a transfer to this new base is accomplished without discontinuities in the command signal. As will be shown below, excellent results can be obtained by transferring the command signal from the control which generated the pattern from the initiation of travel to a control generating a pattern from the destination or final value at a moment when the ratio of the velocity to the distance from the destination has attained a selected value. In the development which follows, it will be shown that this transfer can be efi'ected without ambiguity when the ratio of the pattern velocity to the pattern distance to go to the destination is in the relationship of a/3b where a is the maximum acceleration and b is the maximum jerk or rate of change of acceleration. As viewed on FIG. 10, this transition occurs at the moment I. on the velocity vs. time plot.

The transition of the pattern base from initiation to destination is accomplished by contacts of relay RF when that relay is energized. Energization of the relay is accomplished through a logic circuitry responding to the command or pattern velocity signal X, and the command or pattern position signal X, as compared to the signal X representative of the location of he destination of the moving body. The computed or pattern position represented by the voltage minus X, at terminal 197 is compared with the voltage X at terminal 198 representative of the location of the destination or call request" of the moving body in amplifier A9. The relative values of the voltages and monitored in this and the associated circuits necessary to provide the proper ratio as noted above is adjusted by resistances 199 and 201 and voltage divider 202. The summing which occurs by this combination produces a signal which is representative of the distance between the generated pattern position and the actual destination position. This difi'erence signal is compared with the generated pattern velocity X, in amplifier A10. in order to properly relate these signals and maintain the requisite ratios, the gain of amplifier of A9 is adjusted by means of feedback resistor 203 nd voltage divider 204.

Signal X, is fed to amplifier A10 through resistance 205 and the pattern distance-to-go is fed to A10 through resistance 206. When the two signal values are equal and therefore the ratio specified above is satisfied, absolute value circuit AV4 receives a zero input signal and therefore issues an "on" signal on its inverse output lead 207 to or" 208, which issues a signal to AND 209 over input 211. Signal ST provides a ground to lead 212 when a run is in progress and following the completion of a run until the next run start signal is applied to the pattern. For example the signal ST can be employed as an indication of the proper condition of safeties and interlocks of the system such that it must drop prior to a start signal and should reappear prior to the time the final portion of a stopping sequence is entered upon by the pattern command. Upon coincidence of a start signal ST applied at terminal 212 as a ground, indicating that the system has a signal to run and is in the process of responding to that signal, AND 209 issues an on" signal to Schmitt trigger 210 over its output lead 213. The trigger 210 seals the circuit by applying its output signal over lead 214 to the input or OR 208 whereby AND 209 is sustained as long as the ST signal is maintained on 212. The inverse output of trigger 210 is applied over lead 215 to power switch PS1 which again inverts the signal providing a ground so that relay RF pulls in. Relay RF is supplied with l2 volts DC at terminal 216 and is pulled in whenever the circuit is completed through its coil to ground.

The functions of relay RF when energized are best considered with respect to the terminal portions of the stopping sequence and therefore will not be considered until the stopping distance computer shown in block diagram in FIG. 12 and in schematic form in FIG. 13 is considered. As illustrated in FIG. 12, the signal initiating slowdown is derived from two channels, one representative of a stop signal effective during the period the pattern signal is accelerating and the other a stop signal effective during the interval the pattern is generating the maximum velocity. ln the case of slowdown 

1. An elevator control comprising an elevator hoist motor, an elevator car driven by said hoist motor, means defining a path along which said car is driven, a plurality of stopping stations including terminal stations for said car along said path, means to stop said car at said stations, means to impose a requirement on said car to run toward a terminal stopping station displaced from its current position, means for generating a plurality of signals characteristic of car position at said several stopping stations along said path, destination signal issuing means initially issuing a position signal characteristic of the terminal stopping position, means to register service requirements at each stopping station, means responsive to car position along said path for monitoring the individual stopping station correlated with said car position for demands for service for that station, and means responsive to a demand for service at a monitored stopping station for altering said destination signal issuing means to issue a position signal characteristic of said monitored stopping station.
 2. An elevator control comprising an elevator hoist motor, an elevator car driven by said hoist motor, means defining a path along which said car is driven, means to generate an electrical signal in response to and characteristic of the position of said car along said path, means for generating a commanded position signal as a function of time, said commanded position signal at any instant being characteristic of a position of said car along said path and having a first derivative with respect to time which increases from zero to a maximum value with time in a pattern which is the mirror image of its pattern which decreases from said maximum value to zero with time, means to generate a signal representative of the displacement commanded to achieve said transition of said first derivative from zero to maximum value, means to define a destination signal value for said commanded position signal, means responsive when the difference between said destination signal and said commanded position signal equals said transition displacement signal to initiate the decrease in said first derivative of commanded position signal, means to combine said commanded and said car responsive position signals to produce an error signal, and means responsive to said error signal for controlling said hoist motor.
 3. An elevator control comprising an elevator hoist motor, an elevator car driven by said hoist motor, means defining a path along which said car is driven, means to generate an electrical signal in response to and characteristic of the position of said car along said path, means for generating a commanded position signal as a function of time, said commanded position signal at any instant being characteristic of a position of said car along said path means, to define a destination signal value for said commanded position signal, means to ascertain the signal magnitude representing the commanded displacement required to make the transition of the first derivative with respect to time of said commanded position signal between its current value and zero, means to combine said ascertained displacement signal with said commanded position signal, means to compare said combined signal with said destination signal, means responsive to a predetermined relationship between said compared signals to initiate a decrease in the first derivative with respect to time of said commanded position signal, means to combine said commanded and said car responsive position signals to produce an error signal and means responsive to said error signal for controlling said hoist motor.
 4. A combination according to claim 3 wherein said predetermined relationship between said compared signals is equality.
 5. An elevator control comprising an elevator hoist motor, an elevator car driven by said hoist motor, means defining a path along which said car is driven, means to generate an electrical signal in response to and characteristic of the position of said car along said path, means for generating a commanded position signal as a function of time, said commanded position signal at any instant being characteristic of a position of said car along said path, means to define a destination signal value for said commanded position signal, means to ascertain the signal magnitude representing the commanded displacement required to make the transition of the first derivative with respect to time of said commanded position signal between its current value and zero, means to compare said ascertained signal with said destination signal, means responsive to a predetermined relationship between said compared signals to initiate a decrease in the first derivative with respect to time of said commanded position signal, means to combine said commanded and said car responsive position signals to produce an error signal, and means responsive to said error signal for controlling said hoist motor.
 6. An elevator control comprising an elevator hoist motor, an elevator car driven by said hoist motor, means defining a path along which said car is driven, means to generate an electrical signal in response to and characteristic of the position of said car along said path, means for generating a commanded position signal as a function of time, said commanded position signal at any instant being characteristic of a position of said car along said path and having a first derivative with respect to time which increases from zero to a maximum value with time in a pattern which is a mirror image of its pattern which increases from said maximum value to zero with time, means to define a destination signal value for said commanded position signal means to ascertain the signal magnitude representing the commanded displacement required to make the transition of the first derivative with respect to time of said commanded pOsition signal between its current value and zero during the period the first derivative with respect to time of said commanded position signal increases, means to generate a signal representative of the displacement commanded to achieve a transition of said first derivative from zero to maximum value, means effective during the period said first derivative increases for comparing said ascertained signal value to said destination signal, means comparing said commanded position signal to said destination signal to ascertain a signal difference, means effective during the period said first derivative is at a maximum value for comparing said transition displacement signal with said signal difference, means responsive to equality between said ascertained signal value and said destination signal or between said displacement signal and said signal difference for initiating the stop of said commanded position pattern, means to combine said commanded and said car responsive position signals to produce an error signal, and means responsive to said error signal for controlling said hoist motor.
 7. An elevator control comprising a hoist motor, an elevator car driven by said hoist motor, means defining a path along which said car is driven, means for generating a commanded position signal as a function of time, said commanded position signal at any instant being characteristic of a position of said car along said path and having a first derivative with respect to time which increases from zero to a maximum value with time in a pattern which is a mirror image of its pattern which decreases from said maximum value to zero with time, means to store as an initial position signal said commanded position signal generated during the most recent interval in which said commanded position signal remained unchanged said initial position signal providing a base for subsequently generated commanded position signals, first means issuing a signal in response to the third derivative of said commanded position signal with respect to time, and means to measure the commanded displacement as the difference between said initial position signal and said commanded position signal upon the onset of coincidence of a signal from said first signal issuing means and the absence of a signal from said second and said third signal issuing means.
 8. An elevator control comprising a hoist motor, an elevator car driven by said hoist motor, means defining a path along which said car is driven, means for generating a commanded position signal as a function of time, said commanded position signal at any instant being characteristic of a position of said car along said path and having a first derivative with respect to time which increases from zero to a maximum value with time in a pattern which is a mirror image of its pattern which decreases from said maximum value to zero with time, means to store as an initial position signal said commanded position signal generated during the most recent interval in which said commanded position signal remained unchanged, said initial position signal providing a base for subsequently generated commanded position signals, means effective for an initial period to increase the second derivative with respect to time of said commanded position signal from zero to a predetermined value at a constant rate with respect to time, b, means for maintaining said predetermined value, a, for a second period contiguous with said initial period, means issuing a signal corresponding to the first derivative with respect to time of said commanded signal, and means for computing the signal valve to which said commanded position will proceed subject to the limits of said value a and said rate b if a stop is initiated as functions of said current commanded position signal, said initial position signal, said current first derivative of said commanded position signal, said initial position signal said current first derivative of said commanded position signal, said value of a aNd said rate of b.
 9. A combination according to claim 8 wherein said computed signal valve is dependent upon said current commanded position Xp, said initial position, Xi, said current first derivative of said commanded position signal, Xp, said second derivative of commanded position predetermined value, a, and said rate of change of said second derivative value, b, in the relationship where the quantity 2a3/3b2 is negative for an ascending commanded position signal and positive for a descending commanded position signal.
 10. A combination according to claim 8 including means for storing said computed signal, and means for actuating said storage means in response to the termination of said second period.
 11. A combination for generating AC commanded position signal as a function of time for an object driven according to said signal which comprises means generating an electrical signal which is representative of acceleration a a function of time and is limited during changes in acceleration to a predetermined, constant value of jerk, means integrating said acceleration signal with respect to time to generate a commanded velocity signal with respect to time, means integrating said velocity signal with respect to time to generate a commanded position signal with respect to time, means controlling displacement of said object in response to said commanded position signal, means generating a homing signal following a predetermined transition with time from a first predetermined commanded position signal value to a second predetermined commanded position signal value representing the destination of said object, and means responsive to a predetermined relationship between said commanded velocity signal and said commanded position signal for transferring said means controlling displacement of said object from control by said integrated velocity signal to control by said housing signal generator.
 12. A combination according to claim 11 wherein said acceleration signal is generated subject to constraints of constant rate of change of acceleration, b, and maximum acceleration, a, and said ratio of commanded velocity signal to commanded position signal is according to the relationship a/3b.
 13. A stopping distance computer for a movable object having a plurality of stopping stations, means for generating a characteristic electrical signal for each stopping station, means selecting one of said signals as a destination signal, means generating a commanded position signal as a function of time, means driving said object according to said commanded position signal means developing a signal difference between said commanded position signal and said destination signal to represent the displacement signal remaining to be generated, said commanded position signal having a velocity characteristic which is symmetrical in its transition between zero and a maximum velocity, means to measure the displacement of said commanded position signal required during the velocity transition from zero to a maximum velocity, means to store said measured signal, means to compare said stored signal with said difference signal and means to initiate a pattern commanded position signal transition from maximum to zero velocity when said stored signal and said difference signal have a predetermined relationship.
 14. A combination according to claim 13 wherein said relationship between said stored signal and said difference signal absolute values is equality.
 15. In combination a commanded position signal generator, a stopping signal generator for issuing s stop signal to said commanded position signal generator, means to generate a commanded position destination signal, means to continuously calculate the commanded position signal difference required to make a transition between zero velocity and the current velocity during acceleration of said commanded position signaL by said generator, means to measure the difference signal between the commanded position signal and the destination signal, and means to initiate a stop of said commanded position signal when said transition interval position signal difference has a predetermined relationship to said signal difference between said commanded position and said destination signals.
 16. In combination a command position signal generator, a stopping signal generator for issuing a stop signal to said commanded position signal generator, means to generate a commanded position destination signal, means to continuously calculate the commanded position signal difference required to make a transition between zero velocity and the current velocity during acceleration of said commanded position signal by said generator, means to measure the difference signal between commanded position signal and the destination signal, and means to initiate a stop of said commanded position signal when said transition interval position signal difference equals said signal difference between said commanded position and said destination signals.
 17. A stopping signal generator for a driven object comprising a generator of a commanded position signal as a function of time for controlling the drive for said object, means to generate a signal characteristic of the destination of said object, means to continuously predict the stopping position signal for said commanded position signal when a stop is initiated at any instant and said signal is subject to given acceleration and rate of change of acceleration contraints and means to initiate a stop for said commanded position signal when said predicted stopping position signal has a predetermined relationship to said destination signal.
 18. A stopping signal generator for a driven object comprising a generator of a commanded position signal as a function of time for controlling the drive of said object, means to continuously predict the stopping position signal for said commanded position signal when a stop is initiated at any instant and said signal is subject to given acceleration and rate of change of acceleration constraints and means to initiate a stop for said commanded position signal when said predicted stopping position signal has an absolute value equal to the absolute value of said destination signal.
 19. A combination for computing the instantaneous stopping position for a commanded position signal representing position of an object as a function of time comprising means generating a signal characteristic of the position for said object from which said commanded position signal is initiated, means generating a signal characteristic of the current commanded position signal, means generating a current commanded velocity signal characteristic of that providing said commanded position signal, said commanded position signal being subject to constraints of maximum acceleration a and constant rate of change of acceleration b means to multiply said velocity signal by the ratio of a/b, means to apply a signal having an absolute value of 2a3/3b2 and a sign dependent upon the direction of displacement commanded by said commanded position signal, and means to sum said initial position signal, said current position signal, said product of velocity and the ratio of a/b and said signal 2a3/3b2 to produce a predicted stopping position signal.
 20. A combination according to claim 19 including means to generate a signal characteristic of the designation assigned said commanded position signal, means to compare said destination signal and said predicted stopping position signal and means responsive to a given relationship between said destination and said predicted stopping position signal for initiating a stop of said position pattern signal.
 21. An elevator control for an elevator car driven by a direct current hoist motor, a variable voltage source supplying the armature of saId hoist motor for controlling the speed of said motor, a source of direct current, a potentiometer connected across said direct current source, a wiper for said potentiometer positioned thereon according to the position of said car along its path of travel to issue a voltage characteristic of car position, a series of resistors connected across said direct current source, means to selectively tap voltages from said resistors, each tap being so related to said resistors as to issue a voltage corresponding to the voltage issued by said potentiometer when said car is located at a stopping station corresponding to said tap, a pattern generator for generating a commanded position voltage with respect to time based upon an initial voltage corresponding to the initial position of said car, means to apply a voltage from a selected tap to said pattern generator, means for summing said pattern position voltage and said car position voltage to produce an error voltage, means to control said variable voltage source in response to said error voltage and means to control the magnitude of the voltage applied to said potentiometer and said series of resistors to control the flight interval of said elevator between its initial position and its destination.
 22. An elevator control for a hoist motor comprising a pattern generator for generating a position command signal as a function of time, means to constrain said pattern signal to predetermined, constant values of rate of change of acceleration, acceleration, and velocity, a stopping distance computer generating a signal characteristic of the displacement required by said commanded signal subject to said constraints to complete the transition between zero velocity and maximum velocity, a stopping distance computer generating a signal characteristic of the predicted stopping position throughout the acceleration of said pattern, a call query signal generator generating a signal characteristic of the position of a stopping station for which a call has been registered, first means to compare said call query signal with said predicted stopping position signal during acceleration of said command signal, second means to compare the difference signal between said call query signal and said position command signal with said transition signal during maximum velocity interval of said command signal and means effective while said command signal is accelerating to accept a registered stop signal for said elevator when said first comparison means indicates a predetermined relationship between said predicted position signal and said call query signal and effective during said maximum velocity interval of said command signal to accept a registered stop signal when said second comparison means indicates a predetermined relationship between said call query signal, said position command signal and said transition signal.
 23. In combination means for generating a commanded position signal as a function of time, a driven object, drive means for said object controlled by said commanded position signal, means defining a path along which said object is driven, means for selectively establishing a destination signal representative of a selected position of said object along said path, means establishing a predetermined constant value of jerk for changes in acceleration of said commanded position signal, means establishing a predetermined maximum value of acceleration for periods of constant acceleration of said commanded position signal, means for sensing the sign of the velocity of said commanded position signal, means for detecting a jerk component in said commanded position signal, means for detecting said maximum value of acceleration as a component in said commanded position signal, means for generating a signal characteristic of the predicted stopping position signal for said commanded signal, and means for initiating a stop of said commanded position signal upon a coincidence of a positive velocity, either a detected maximum value of acceleration or a deteCted jerk as a component in said commanded position signal and a predicted stopping position signal equal to or exceeding said destination signal.
 24. In combination means for generating a commanded position signal as a function of time, a driven object, drive means for said object controlled by said commanded position signal, means defining a path along which said object is driven, means for selectively establishing a destination signal representative of a selected position of said object along said path, means establishing a predetermined, constant value of jerk for changes in acceleration of said commanded position signal, means establishing a predetermined, maximum value of acceleration for periods of constant acceleration of said commanded position signal, means for sensing the sign of the velocity of said commanded position signal, means for detecting a jerk component in said commanded position signal, means for detecting said maximum value of acceleration as a component in said commanded position signal, means for generating a signal characteristic of the predicted stopping position signal for said commanded signal, and means for initiating a stop of said commanded position signal upon a coincidence of a negative velocity, either a detected maximum value of acceleration or a detected jerk as a component in said commanded position signal and said destination signal equal to or exceeding said predicted stopping position signal.
 25. In combination means for generating a commanded position signal as a function of time, a driven object, drive means for said object controlled by said commanded position signal, means defining a path along which said object is driven, means for selectively establishing a destination signal representative of a selected position of said object along said path, means establishing a predetermined, constant value of jerk for changes in acceleration of said commanded position signal, means establishing a predetermined, maximum value of acceleration for periods of constant acceleration of said commanded position signal, means for sensing the sign of the velocity of said commanded position signal, means for detecting the absence of a jerk component in said commanded position signal, means for detecting an absence of an acceleration component in said commanded position signal, means for storing as an initial position signal the commanded position signal issued during the immediately preceding interval of constant commanded position signal, means for storing a slowdown displacement signal ascertained as the signal difference between said initial position signal and said commanded position signal at the instant an absence of an acceleration and jerk component in said commanded position signal is detected, means for measuring the commanded distance-to-go as a difference signal between the commanded position signal and said destination signal, and means for initiating a stop of said commanded position signal upon a coincidence of a positive velocity, an absence of a acceleration component in said commanded position signal, an absence of a jerk component in said commanded position signal, and a slowdown signal equal to or greater than said distance-to-go signal.
 26. In combination means for generating a commanded position signal as a function of time, a driven object, drive means for said object controlled by said commanded position signal, means defining a path along which said object is driven, means for selectively establishing a destination signal representative of a selected position of said object along said path, means establishing a predetermined, constant value of jerk for changes in acceleration of said commanded position signal, means establishing a predetermined, maximum value of acceleration for periods of constant acceleration of said commanded position signal, means for sensing the sign of the velocity of said commanded position signal, means for detecting the absence of a jerk component in said commanded position signal, means for detecTing an absence of an acceleration component in said commanded position signal, means for storing as an initial position signal the commanded position signal issued during the immediately preceding interval of constant commanded position signal, means for storing a slowdown displacement signal ascertained as the signal difference between said initial position signal and said commanded position signal at the instant an absence of an accelerated and jerk component in said commanded position signal is detected, means for measuring the commanded distance-to-go as a difference signal between the commanded position signal and said destination signal upon a coincidence of a negative velocity, an absence of an acceleration component in said commanded position signal, an absence of a jerk component in said commanded position signal, and a distance-to-go signal equal or greater than said slowdown signal.
 27. A control for an elevator hoist motor driving an elevator car comprising means to generate a voltage signal characteristic of the present position of said car along its path of travel, means to continuously generate during the running of said car a voltage signal characteristic of the stopping distance required, means to indicate a terminal station as the destination for said car during a run as a voltage signal characteristic of the car position when at the terminal station, means to impose stop commands for car stop stations intermediate said car and said terminal, means to monitor said stop commands during the advance of said car toward said terminal, means responsive to the advance of said car to intermittently generate a voltage representative of the position of said car stop stations, means responsive to a coincidence of a predetermined relationship between said current stopping distance voltage and said current car stop station voltage and the existence of a stop command for said station to transfer said indicated destination voltage from that for said terminal station to that for said current car stop station.
 28. A combination according to claim 2 including means to constrain the signal changes from said generating means for said commanded position to signal to a constant value of jerk, to a maximum value of acceleration, and to a maximum value of velocity.
 29. A combination according to claim 4 including means to constrain the signal changes from said generating means for said commanded position signal to a constant value of jerk, to a maximum value of acceleration, and to a maximum value of velocity.
 30. A combination according to claim 5 including means to constrain the signal changes from said generating means for said commanded position signal to a constant value of jerk, to a maximum value of acceleration, and to a maximum value of velocity. 